When we talk about the scalability for a web application, it is quite common for us to think of load balanced web farms. This obviously will require the application session state be managed using one of the OutProc options. Depending the utilization of the session state data and the implementation approach, the state server (be it state service or SQL server) may soon hit the scalability / performance limits and become a bottleneck.
This prompted me to think about possible scalability and availability solutions for the State Server. It is again possible to have a load balanced farm of servers to serve the session state requests. But, this requires the state information is replicated across all such servers, so that the information will always be available in across all the load balanced state servers. Obviously this is additional overhead. There are third party tools(like scalenet) to have the session and cache information replicated across multiple servers.
As I was looking for an alternative solution, just came across this Best Practices article on state management published by Microsoft. This article suggests a simple approach of session partitioning using the PartitionResolver Interface and determining the partitioned server using a key derived from the session id.
If any of you have implemented this or any other approach, do post it here.